The identification of refrigerant in a refrigeration and air-conditioning system is critical and failure to do so often results in difficulties. Adding too much refrigerant to the system may cause operating inefficiency, system failure, and can lead to broken tubes, fittings, and component failure due to over pressurization. A misdiagnosis of an undercharged system caused by the leaking out of the refrigerant often delays repairs. Liquid indicating sight glasses are used to allow a person to visually monitor the level of the refrigerant in refrigeration and air-conditioning systems. These sign glasses require a light source to be read correctly. The reading must be done in close proximity to the sight glasses in order to determine the presence of refrigerant in the refrigeration and air-conditioning systems.
Liquid indicating sight glasses have historically consisted of flat glasses in gasketed metal fittings that allow the inspection of the interior of a vessel or tube. Refrigeration and air-conditioning sight glasses are manufactured by fusing glass into a steel fitting. An example of this sight glass is disclosed by B. Bowsky and G. J. Scilito in U.S. Pat. No. 5,383,338. A hand-held flashlight or other light emitting device is used to direct light through the glass to identify the presence of clear or slightly translucent fluids in a vessel or tube. The difficulty with these sight glasses is that, while they can clearly identify a partially full condition, where the sight glass is only partially covered, they can be easily misread when completely full or the level of the liquid is below the bottom of the sight glass. This misreading is of particular concern and most indicative of an inexperienced observer or technician.
Alternatives are presently available such as a sight glass that has a propeller inside the sight glass that rotates when there is liquid flow. There are also sight glasses that use a series of horizontal prisms on a front sight glass that distorts the image, such as the word “FULL”, printed on a surface behind the sight glass. When the narrow space between the sight glass and the surface is filled with liquid, the word “FULL” is clearly visible.
R. L. Nagel in U.S. Pat. No. 2,943,530 discloses a liquid level indicator for providing an optical stimuli as a function of electrolyte level in a battery. The level indicator is a post joined to a battery cap. The lower end of the post has a lateral extension and a notch equal to the diameter of the post. The notch is defined by plane angular and longitudinal surfaces. The bottom of post is colored green. The outside lateral surface of the extension colored red is located in lateral alignment with the upper angular surface of the notch. When the notch is full of electrolyte, the color green will be observed by viewing the top of the cap. The color red is observed when the level of the electrolyte is below the upper angular surface of the notch.
A. H. Kelch, Jr. in U.S. Pat. No. 3,589,191 discloses a reflective gauge that provides a visual indication of the volume of a liquid in a container, such as a gas tank. The gauge has transparent, spiral-like member having a plurality of stepped prismatic facet elements. Light is not reflected through the facet elements which are immersed in liquid. Light is reflected through the facet elements located above the surface of the liquid thereby providing visual information concerning the volume of liquid in the container.
R. J. Dillon in U.S. Pat. No. 6,578,418 discloses a sight glass apparatus for providing visual information regarding the level of a liquid in a tube. The sight glass has a transparent body with a convex lens and a concave lens at opposite ends of the body. The body has V-shaped grooves open to opposite sides of the body. A color pad on the concave lens is viewable at the convex lens when the tube is full of liquid.